1. Field of the Invention
The present invention generally relates to a power semiconductor device, and particularly to a joint assembly structure of an insulating substrate and electrode terminals of a power semiconductor device used in a power converter or the like.
2. Description of the Prior Art
A power semiconductor device (hereinafter, referred to as “semiconductor power module”, or more simply “power module”) is generally arranged to convert a direct current input into an alternating current output of an arbitrary frequency by using a semiconductor element, and is employed in, for example, an inverter used for motor control or different purposes and also for use in an uninterruptible power source (UPS).
In a conventional semiconductor power module, a semiconductor (element) chip is fixedly mounted onto an insulating substrate and one end of each electrode terminal is fixedly joined to a specified portion on an upper surface portion of the insulating substrate through a joint material, and an electrode terminal plate is extended to be directly connected to a circuit pattern.
In order for preventing a breakage of a joint portion between the electrode terminal and the insulating substrate in the presence of a stress caused through temperature changes or similar factors, an S-shaped structure is employed for the electrode terminal that is fixedly attached to the insulating substrate to thereby achieve a stress relaxation structure (see, for instance, Patent Reference 1: Japanese Utility Model Laid-Open Publication No. 5-15439 (1993)).
There is also disclosed an arrangement for achieving stress relaxation by extending each electrode terminal in a plate beam-like manner (see, for instance, Patent Reference 2: Japanese Patent Laid-Open Publication No. 10-173126 (1998)).
In another disclosed arrangement, a clearance is provided in a non-fixed condition between a surface conductive pattern of the insulating substrate and the insulating body, and electrode terminals are joined to the conductive pattern to thereby achieve the stress relaxation. Alternatively, such a clearance is formed to be large so as to easily discharge residues occurring during manufacture of the power module (see, for instance, Patent Reference 3: Japanese Patent Laid-Open Publication No. 2001-68623).
When assembling such a semiconductor module of the above arrangement, the electrode terminal plates and the semiconductor chip are electrically connected where the electrode terminal plates form a laminated structure together with the insulating layer disposed underneath thereof while the electrode terminal plates are insulated from each other.
Each electrode terminal plate extends outside of a resin case to form, for instance, a P terminal, an N terminal or an alternating current terminal of main circuit terminals for external connection, on an upper surface of the semiconductor power module. It is noted that a filler material such as silicon gel is filled in an interior space surrounded by the resin case.
However, in the conventional semiconductor power module as disclosed in Patent Reference 1, stress relaxation is achieved by forming electrode terminals to be of S-shape for preventing breakage of joint portions between electrode terminals and the insulating substrate. Therefore, there arise drawbacks such that the electrode terminals will be of elongated shape in the height direction which is inconvenient in view of reducing the size of the power module and which also leads to cost up of the electrode terminals.
In the arrangement as disclosed in Patent Reference 2, stress relaxation is achieved by extending the electrode terminals in a plate beam-like manner such that the electrode terminals become long in the horizontal direction. This is problematically inconvenient when considering reduction in size of the power module.
On the other hand, in the arrangement disclosed in Patent Reference 3, the electrode terminals are joined with the surface conductive pattern of the insulating substrate while the surface conductive pattern and the insulating body are in non-fixed condition, and therefore fluid or gas used during manufacturing processes of the power module will remain in the non-fixed portions. Thus, there arise drawbacks such that, when such residues are dispersed in the power module during use thereof to thereby affect characteristics of the semiconductor chip.
In an arrangement in which the clearance of the non-fixed portion is formed to be large for easily discharging such residues during manufacture of the power module, there arise drawbacks such that thermal conduction for discharge heat from the metallic substrate generated in joining of the electrode terminals is undesirably blocked by the clearances of non-joined portions, which makes the joining of electrode terminals difficult and accordingly degrade the production efficiency.